linux-kernel - Re: [PATCH -v3] x86: do not free zero sized per cpu areas

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Date:	Fri, 19 Mar 2010 15:21:33 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	Ian Campbell <ian.campbell@...rix.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH -v3] x86: do not free zero sized per cpu areas

On 03/19/2010 03:18 PM, Yinghai Lu wrote:
> From: Ian Campbell <ian.campbell@...rix.com>
> 
> This avoids an infinite loop in free_early_partial().
> 
> Add a warning to free_early_partial to catch future problems.
> 
> -v3: according to hpa, don't bother caller.
> 
> Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> ---
>  kernel/early_res.c             |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/early_res.c b/kernel/early_res.c
> index 3cb2c66..f3a861b 100644
> --- a/kernel/early_res.c
> +++ b/kernel/early_res.c
> @@ -333,6 +333,11 @@ void __init free_early_partial(u64 start, u64 end)
>  	struct early_res *r;
>  	int i;
>  
> +	if (WARN_ONCE(start >= end,
> +		      "free_early_partial got wrong start/end %#llx/%#llx\n",
> +		      start, end))
> +		return;
> +
>  try_next:
>  	i = find_overlapped_early(start, end);
>  	if (i >= max_early_res)

No, that's wrong.

The workaround is still needed for the case of equality to avoid the
infinite loop.

So you need an:

	if (start == end)
		return;

	-hpa
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